Deltas are dynamic environments
where morphological changes occur at human time scales (50-100 yr), and where intense
biological and geological interactions are still evident in the fossil record. When
adding human impacts into this complex equation, as for example the
transformation of natural wetlands into rice fields, deltas can be considered
“natural laboratories” to study changes over historical (millennia) and recent (decades)
periods. This information can be then used for proposing management measures to
mitigate ongoing and future climate change impacts.

The Ebro Delta (NE Iberian
Peninsula) is one of the most ecologically important coastal wetlands of the
Western Mediterranean due to its faunal and vegetal biodiversity. In addition,
it supports an important economic activity for the regional population by means
of rice agriculture, tourism and coastal fisheries.

Despite that the ecology of the
Delta has been largely studied since the 1980s, there is a lack of scientific understanding
about its natural and human-driven evolution at millennial and
decadal-centennial time scales. This necessity is also justified by the fact
that hypothesis about the Ebro Delta’s origin was exclusively based on personal
interpretations from Roman written records.

Paleoecology provides reference conditions for those degraded habitats, which can be used as a benchmarks to restore and mitigate human-induced and sea level rise impacts

Recently, a new paper has been
published to study the present and past Ebro Delta habitats from a
paleoecological perspective (the paleoecology is the ecology of the past). This
work summarises the PhD thesis of Dr Xavier Benito, which was developed at IRTA
(Research Institute for agricultural and food technology, Sant Carles de la
Rápita – Tarragona – Catalonia). For each of the two temporal windows,
different methods were applied: i) at the present, the utility of diatoms (unicellular
algae) and foraminifera (unicellular protozoa) as ecological indicators of the
habitats, and ii) in the past, the use of fossil foraminifera to reconstruct
natural (origin and evolution) and human-driven changes (rice field
colonization).

The leading author, Xavier Benito,
claims that their results showed that Ebro Delta originated at least 8,000
years ago – since only deltaic habitats were identified in the sediments at
that time, rejecting therefore the reining hypothesis about the delta’s Roman
origin.

Habitats identified according to
diatom composition and abundance in the Ebro Delta samples, and Holocene (last
12,000 years) evolution of the Ebro Delta as reconstructed from
micropaleontological fossil record.

These results
have clear implications in the context of current climate change impacts.
Basically, bringing the Delta’s habitat to a good ecological condition can
increase their capacity to cope with future changes, such those resulting from
climate change. We should consider that climate change projections predict an
increase in sea level and a reduction in the Ebro’s discharge and sediment
loading. The long-term perspective provided here shows how the most “natural”
Ebro Delta could cope with past climate changes, which probably implicated
higher sea level fluctuations than those projected by the end of the 21th
century: more than 0.5 m (it should be noted that around 60% of the Delta lies
below 0.5 m of surface elevation).

Fossil microorganisms revealed that the Ebro
Delta originated at least 8000 years ago

Fortunately, it
is not needed to go back 8,000 years in the Delta’s history to find such
natural habitats. The results also showed that just 150 years ago, before the
proliferation of rice cultivation, habitats were hydrologically connected with
the sea and characterized by high diverse foraminifera communities. These
conditions can be used as a benchmark to assess which habitats were deviated
from its natural reference conditions (high ecological status) as result of
rice colonization in the Delta. Only then, stakeholders can use this
information to restore habitats supported by natural fluxes of water and
sediments in order to mitigate potential wetland loss due to sea level rise.